Governing mechanism for extracting type turbines



Aug. 29, 1950 c. E. SEDERQUIST 2,520,568

GOVERNING MECHANISM FOR EXTRACTING TYPE TURBINES Filed Aug. 28, 1948 Y e m e g ,0 Z. w W A I S W Patented Aug. 29, 1950 GOVERNING MECHANISM FOR EXTRACT- ING TYPE TURBINES Carl E. Sederquist, Melrose, Mass, assignor to 7 General Electric Gompanygja corporation. of

New York Application August 28, 1948, Serial No. 46,596

'6 Claims. 1

This invention relates to a governing system for an elastic fluid turbine of-the extraction type, having an inlet valve for controlling the admission of motive fluid to a high pressure turbine section in series flow relation with an extraction valve for admitting steam to a low pressure turbine section, the interaction of these two valves determining the energy output of the turbine rotor and the rate of flow of elastic fluid taken from the turbine casing through an extraction opening located between the high pressure turbine section and the extraction valve. The in-'- vention constitutes an improved governor of the so-called three-arm" type, and is a further improvement of the three-arm governing mechanism disclosed in United States Patent 2,095,860, patented October 12, 1937 on an application of F. R. Ericson. I

With extraction governors of the three-arm type previously known, it has been necessary to make a number of adjustments in the vari-' ous linkages in order to alter the desired pressure to be maintained at the extraction opening over a wide range without introducing substantial deviations from the theoretical optimum opera tion of the governor. Such adjustments could not be made while the machine was in operation. Furthermore, the earlier three-arm governing systems have included means for preventing "overtravel of the steam valves in the closing direction, in order to provide proper operation and prevent mechanical damage to the linkages connecting the various components of the system when hydraulic servo-motors are employed to' readily made adjustments, the extraction pres- I sure may be conveniently varied over a wide range ,without shutting down the machine and without re-adl'usting the overtravel preventin mechanism.

Other objects and advantages will be apparent to those skilled in the art from the following description taken in connection with the accom-. panying, drawing in which the single figure isa diagrammatic representation of an elastic fluid turbine having an improved threearm governing-- mechanism in accordance with the invention.

Referring now more-particularly to the drawing, the invention is illustrated as applied to an:

elastic fluid turbine I supplied with motive fluid from a high pressure boiler 2 through a conduit 3 containing a high-pressure inlet valve 4. The-- turbine l includes a high-pressure section la and a low-pressure section lb, each including one' .or more nozzle diaphragms and bucket-wheels. s'

Intermediate the high and low-pressure sections is an extraction opening 5 communicating with a conduit 6 arranged to deliver motive fluid at an intermediate pressure to any suitable con-' .sumer, indicated diagrammatically at i, and to which-additional steam may be supplied by a low-r.

pressure boiler 8. J Flow of motive fluid through the low-pressure turbine section lb is regulated by an extraction valve 9. Fluid discharged from Y the low-pressure section lb into exhaust hood It) may pass to a discharge conduit ll thence to a condenserIor to some still lower pressure turbine;

element, which may be on the same shaft ,le of turbine l or may constitute a separate tur-:

bin'e in series flow relation with turbine l Rotor I0 is connected to' a suitable load. output device indicated diagrammatically as an electric generator I2.

It will be appreciated by those familiar with l prime movers of this type that the turbine I is intended to perform two important functions;

(1) generation of ,mechanical shaft power for driving the load l2, and (2) supplying .steam' at a desired intermediate pressure to a consumer I, which may represent some industrial processor heatingsystem. The auxiliary low-pressure boiler 8 is arranged to supply steam to the con-. sumer 1 when thedemand for process steam exceeds that which can be supplied by the highpre'ssure boiler 2. The low-pressure boiler 8 also suppliessteam through the extraction opening 5.

to the low-pressure section of the turbine whensure but at a variable rate determined by the operation of the consumer, the low-pressure boiler The flow arrows shown in' value 7 rechiireii lb'y ithe (consumer il while deniving us'efu-l energy-for the consumer l=2 *in the 7 process. The loW pressure orextraction valve 9 is automatically positioned by the governing system so as to maintain a preselected :mflssuneat the extraction opening regardless of the flemands of the consumer 1 and load device 12.

The governing system shown in th'e firavfimg includes a number of component partscemrnon to the three-arm regulating systems used in the past, as illustrated in the above-aneutiorredmaterrt to Ericson 2,095,860, also the later patent toEricson et al. 2,111,420, patented March 15, 1.9843. These common elements include a speed sensitive 4 hydraulic servo-motor arrangement, and it will be readily appreciated that movement of pilot valve to the right eflects supply of motive liquid from conduit 3| to power piston 29a, the resulting movement of piston 29a to the left against the bias of spring restoring pilot 30 throughllever "34 so that ith'e supplyrof ,motive fluid is discontinued. =Bikewise movement o'f =pilot 30 to the left permits motive liquid to drain to conduit 35, piston 29a bein then caused to move to !the ,r-lightbylthe-spring 36, while the lever 34 again restores ;pilo't 30 'to the aligned position shown in the drawing.

"The alziove--1:iescri'be':l conventional elements of this governing are equivalent to the various arrangements shown in the above-mentioned l2,lll5 ;860 and 2,111,420, and it will be apdevice'a'esponsive toithre speed *of mtor la: and ii lustra'ted diagrammatically as :a centrifugal agavern'or {I 3 a dap'ted to the driven at a speed :pmportienal to that of the turbine shaft; as by any stritalblegearirrg (ndtrshomni) -'-GDVBIZ1'101 2H3 actue mediate point of :a lever Hi5 lfiulommed azt me and on' a :speed adiiustingsor fsymchmziizing device i6, which mav ihe :adtuated'seither day a hand-'xvheel :l'lia .ur a :tzemdtely actuated :positioning :m otor :l fib. 'HIhe rather 12nd :of Elever connected :by a lr. as the intersection :or common rpoin represented shy the pivot Izlza @f a floating :thmee-mrnm flBl/YBI imdicated generally at l9. mhe am Alliamfdahis tfhree-samn :leverzls arranged to actuate tl're ihigh-rpressure inlet valve 4 fby'meansrofiailink :Eilrpivnted to a :lever 21 happo'rted on a fixed il ulcrum :22, 1fhe valve stem 4a being connected :to an iiniiermediate'qmmt (Elf the lever I21. The-(second arm :llgb f "the three-am lever positions ith entraetiohval've 9 by .means" of :a link 23 connected to an intermediate :portion of :a Elever 124 (connected toihhe zs'tem r9a nf the extraction :valve. Therother eml'rof ilesver M'is fixed. The arm 'I-Q'c 19f Ethe floating threearm lever arremgedxtc ibe :positioned in accordance with the extraction pressure intermediate the high land low xpizessure :sections [of the turhme by means ofa rpmssure respensivedev-rce.

a suitable source, for instance a pump (not shown) fromttlretturhirreLshaft, to the ihydraulicmotorapiston 129a. .Pistoolflaalias sawed 32 carrying :a guide qnenfzzxer or make 133 engaging a spherical portionza't'rthe end of lever .arm I suriha manner that vzenliicazl of the three-(arm l'lever 3| 9 is .inemnitted-zunder the action:- of the speed governor 1:3, whileitransverse rmovemerit of the yoke 33 produces notational movementrof .thellever :15 iaboutlthe common point 1:8.

lever 34, and a restoring action is produced on thegpilet valve 88 by reason ef :the iaetlthat lever Mas-also pivotal-1y connectedto the rod 532. i

combination of elementscenstitutes a well-known trod 3'3.

the springs 39a, 39b is su'fficieritthat the axis of the hub portion '58 is ordinarily fixed in space,'but

preciated by those familiar with extraction governers-ofthis type that the function of the speed governor is is to hold the turbine rotor speed constant, rat :a value sselecimrl :by the synchronizing device :15, ihy impamingstnaaislartimial movement ito the tlm ee-earrn lever I19 in a'vertical reclii'on; while the extraction pressure tresponsivedevice 25 pmduces rotaltionalnnovement of the three-arm lever about the. acommon point Translational movement 2a wenfiical direction.

metres :both valve stems 4a, :9a the same direotion simultaneously soiasito vary :the how'throu the'zhigh and low :pressure elements and change the ;load (output thereof, while rotational movement-20f ithe :three-rarm mositions valve 14,! in opposite directions in "order to :keep the extractionpressume constant. Thea-hove elements and their methud -of operation have been sufiioiently described "in the previous patents so that more 16 tailed-description here seems unnecessary.

The present invention includes a special air-i rangementrfor gpreventingtovertravel ef :the valves 4, -9 in :both ;the :o peninguand the :olosing directions.

prevent ldeiormation of the mechanical pa-rts pf the various linkages which .might occur if the, powerful hydraulic motor '29 z-tried to move either of the valves in the elosing direction when the, vahae .disk was already against its :seat memloer,;- or conversely tried to :move .the valves iarther in the opening direction beyond thelmaximum opera. The arrangement ior effectingthis position.

over'travel limiting function is as .follows.

.A second three-arm lever" indicated generally 7 at 31 is supported adjacent the first three-arm lever I19.u Lever .31 is not free floating in .the

.same sense as ilever I9, being suspended resiliently from a fixed bracket 38 by means of .a' through-bolt or .rod 39 having a pair of springs.

39a, 39b interposed between a hub portion 31) of lever 57] andfixedabutments at both ends of the With this arrangement, the stiffness of may move a limited amount 'translationally ina vertical direction *when compelled to do so hy 'interaetion df the various components 'of the system It will of course beebv ious that'other types of resilient-supports might 'beemployeti to main tain the hub All ordinarily while pernrl ttin'g-fcertain yielding -under overloads to prevent deformation of the levers and links.

The first anm '3flra'zof the floating lever 33' is adapted ;to be engaged b-ysa'ipa' ir cfi normally fi-xed but adjustable, stops -41; $2, each of which may This has :been hound desirable order to provide proper operation =o-f ithe governor and :to v

rod 43, the latter being pivotally connected to a" bracket or abutment'44 fixed to the-link20; The threaded stops 4|, 42 may be provided with-a lock nut, as indicated at Ma to hold them-firmly in a desired position. While this adjustable stop arrangement ma take many mechanical forms, perhaps the simplest in that shown in the drawing; in which the threaded rod 43 projects freely through a hole in the end of arm 31a, with sufficiently generous clearances that the arm will -The third arm 31c of the second floating leveris- -pivoted to a link 49, which at its other end is connected to the pivot 50 of lever 34. Thus itwill be seen that vertical movement of rods 20,

23 -may under some condition of operation cause one of'the adjustable stops 4|, 42, 46,41, to en gage the respective arms 31a, 31b, so as to rotate the three-arm lever 31 about the fulcrum 40a,- with the result that the rod 49 exerts a restoring. the

efiect'on-the pilot valve 30, thus modifying action of the hydraulic servo-motor 29. T

It may be noted that the link 34 is not con nected to rod 21 by a fixed pivot but through a bottled spring arrangement consist ng of a sleeve 21a loosely surrounding rod 21 and'having trunnions pivoted inthe forked end of lever 34.

A pair of stiff coil springs 2'") are interposed between the sleeve 21a and spaced abutments 21c on rod 21. With this arrangement, the springs 21b ordinarily hold the sleeve 21a in substantially fixed relation relative to rod 21, but some is permittedrelative movement therebetween when the other components of the system compel such displacement. This bottled spring arrangement, and the similar springsuspens'ionfor the-three-arm lever 31, prevent'deformationfof' the linkages.

The arrangement for ily varied; and (b) means for readily adjusting the effective length of the lever 24. 1

= The first'of these adjustments is made possible by the fact that the'arms Sea, I91) are in the form of a single rod having an intermediate threaded portion 5| while the third arm I90 is provided withan end portion 52 having a transverse borethreadedly receiving the rod portion 5|. 'With this arrangement, the arm |9c can be shifted Ion-'- gitudinally, so as to change the length'of' arm I'Q'arelative to I91), by rotating the member Illa, 5|,'-|9b about its own axis by means of an ad-" justing hand-wheel 53. In order to permit this rotational movement,'the connection between the end'of the arm |9a and rod 20 andalso that beown' axis. a

- To facilitate adjustment of the arm I90 on the threaded portion 5|, an'indicator arm 54 is fastened to the end portion 52 of arm l9ca nd car ries a pointer cooperating with a scale 55 marked second floating- 'ermitting adjustment of" the extraction pressure during operation of'the turbine'includes (a) an adjustable arrangementby which the relative effective lengths of the arms I912, IBbof the floating three-arm l9 can be read-" adjustable fulcrum, as follows.

on the' rod 19a)" This scale 'may conveniently be calibrated and marked to read directly in pounds per'square in'ch gage pressure at the extractionopening '5 in turbine I Although difficulty to show clearly in a two di-" mension'al drawing, it will be understood that the three-arm lever'l9, links 2! Rare in a; plane nearest theobserver, the second three-arm lever 31, rods43, 45, 49 are behind, all so arranged that the upper ends of rods 43, 45 will notinterfere with the .free floating movement of the three arm l9, and. the lowerstop 41 on roll 45 will not en-.

gage the link 49'.

The. second adjusting feature, for varying the elfective length of, the lever 24, consists of an The pivots 25. are in the form of trunnions fixed to a cylindrical member 6|] through the bore of which is slid-,

ably disposed the end of rod 24, Sleeve 6|! may. beclamped to red 24 in various adjustedposie. Trunnions tionsby-means of a thumb screw 6|. 2-5 areoarried in a U-shaped bracket secured to a block 52 which is arranged to travel transversely wheelcm. be manipulated tomove pivot 25, longitudinally of rod 24 until the indicating mark on} the Lblock 62 is opposite the desired extrac-.

tion pressure on the scale 56, which scale may i be marked onan adjacent surface of the fixed support- 64. 'With this arrangement, the fixed fulcrum 25 may be readily adjusted so as to vary the effective length of lever 24, and thereby alter the rate of movement of valve stem 9a for a given change in position of the floating three.-'

.-. m'ents, my improvedre'gulating system maybe readilygchanged during operation of the turbine so as to vary the extraction pressure atthe port 5' without introducing. substantial deviations from the theoretical optimum operation of the governor. Thus changes in the'pressure requirements of consumer 1 may be conveniently met by a very simple adjustment of the regulating system.

The operation and use of the system is as follows. ordin'arilyythe adjustable stop 45 will be set so that it just touches the upper surface of leverarm' 31b when valve 9 is in the fully closed position, and the pilot valve 30 is aligned, as in the drawing, so that no liquid is bled from'or supplied to the hydraulic motor 29, and with the piston 29;; in its extreme right-hand position, as shown." With this'adjustment, the operation is as followsi Assume that-the turbine is operating with"the high-pressure inlet valve 4 Wide openjjthe' extraction valve 8 closed and piston 29a in its extreme left hand position, which means that the how through the high-pressure turbine section and outthe extraction opening 5 is just si'ifiici'ent to'satisfy the-mechanical load called for by the speed governor l3 andthe' extraction summons;

7 werdlysuficat have: 1 i'pivots ahout its flxeddeftend andiink it causes the floating threee arm lever :ls-to :begrtnto descend. :SinG8iflE1ad* justable stop 46 was already incontact with the upper-surface of iever 31:; any movement of link :23 downwardly. immediately causes the :s'kop 16 to eiiect clockwise rotation of the times-am lever: 3! about its fulcrum; 48a. This clockwise movement -.causes link 9 to move pilot 30 torthe 1eft,:1:ever 3d allowing this movement due to the: bottled spring arrangement, so operating liquid is bled from the hydraulic motor 29 through drain conduit 35. This causes piston 2.921150 move to the "right and the guide memher 33 acting on the three arm lever 19:: causes flatter to rotate counterclockwise about its pivot point 18, with the result that the armlfib risesto its original position and in doing so raises stop Q6, reIeasing pressuie "on l'ever' arm are, permitting pilot valve 30 to return to its crigmal aligned position by movement of piston 29a to the night. While these actions have been descrmed sequence in order to illustrate the operation, it will he appreciated "that "they-actua1- 1y occur simultaneously so that the net efiect of the adiustah-l'e stop F6 has been to cause the right-hand end *of lever arm 1% to remain fixed in space. Thus, there is no tendency for the *extraction'vaive '9 to move in the closing direction past the fully closedposition, and the forces exe'rte'd by the powerful hydraulic motor 29 are n'dt pennitted to deform-any oi theilinks-orlevers by trying to force the extraction valve past its closed position.

The eifect of the a'djus'tahle stop '1 will be seen from the foliowing. Assume that the inlet valve 4 is fully closed, with steam being supplied. into the extraction. opening '5 from "the low-pressure boiler 8, the extraction valve 9 being wide open so that the steam flow from the "boiler .8 through the low-pressure turbine section lb is just suificient to satisfy the mechanical load requirements of the device ll, the governor 13' again holding the speed constant at .a desired value. Vfith these conditions, the adjustable stop '41 is brought up until itjust touches the underside of. the lever arm .31. This stop will now-prevent overtravel of extraction valve .9 .in the opening directionin the following manner. Assume that the output load on the turbine shaft to increases, so that the speed tends to decrease. speed governor [3 then causes the .rod 14 to move :up-

wardly so that lever i5 rotates counterclockwise about .its leit-hand end, the link all causing the. floating three-arm lever is to rise. Any movement upwardly oi the right-hand end of lever arm L82) causes the stop 4 to engage the-underside oilszver .arm causing the latter to .mtate counterclockwise about its pivot point 40a, with the vresnltthat link 49 causes pilot valve (in to move to the operating ii uid to besupplied from conduit 31 to the piston 29 withtheresult that guide member 33 moves to the left and the floating three-armiever Ill ro tates clockwise about its common point is. :As'

' ta satisfy the demand for mcreased;me.ielsiani'calshaftoutput.v

In this? manner, the stops '46, 4'! prevent inven-v travel of the low-pressure extraction valve d both the openin and the closing With respect to the inlet valve 4, the of thestop 4i :is-as follows. Suppose high-pres- SW6 valve vl is fully closedand steam is being admitted through extraction opening 5 with :vazlve 9 wide open and stop H adiusted :to

touch the upper side of lever 31a. If, new,

shait load oil-put and speed should changeso ose to cause link I! to lower the common pointxmofi floating three-arm 19, any resulting downward movement of link so ill cause th Step4} to rotate the lever -37 counterclockwise-about itspiw 0t 48a. causes. pilot valve on to move to the right, again admitting operatingliquid to ton 29a so that floating =three-sarm :19 is motnted about point 18, with the result thatmm Hid is returned to its original position. ln nther' words, the efiect oi the stop M is to prevent-ans? further net movement downward oi the salve stem to. Thus, =overtravel of the valve 4' in the closing direction is prevented. Similarly, the

adjustable stop 42 may be positioned seas to Gib. gage the underside of layer arm 33a in ordieriao prevent rnnvement of valve stem ts in the=open-- ing direction when the valve '4: is already tally open and the extraction valve s is tully closed.

Experience with regulating systemsincorporating the invention has disclosed. an important advantage of the adjustable steps 41, 42, 416, 4%, in. thatthe speed regulation of the governing sys tom remains exactly constant tor all chopspeed whichoccursirom full load to'noioad,

. change being ordin-ar-ily about 4 per cent ofthe before, the net .efiectzof these interactions isthat So- -;does not; tend to movein the opening dime tion past the iully opened position; but thiscall.

for increased shaft output .is satisfied by clock wise rotation of the floating three-arm. 1.9 sons to partially open the inlet valve 4. Steam trom thehighmressune boiler .2 thenflows the normal rated speed. This speed ohangeis required for "effective operation oi the speed 2msponsivecentriiugal governor t3, For a number of reasons which need not be described iii-detail here, it is very desirable that this regulation always be of the same magnitude regardless of the method of operation. of the turbine.

As indicated above in the description-oi 411528 paratus, the extraction pressure which the activerni-ng system will maintain is varied by changing relative effectivelength oi the lever arms Ha, 19b. In order to increase the extraction pressure, the hand wheel :53 is rotatedto cause arm 190 to shift :to the right on the :portion 5L thus increasin the rate :of movementoi the .inlet valve stem lei-tor a given movement-oi the extraction valvesstem 9a. order to make the system operate properly, it is also necessary to an accompanying adjustment inthe efiective length of the lever 24. When increasing theextraction pressure, the fixed fulcrum :25 must be moved to the right so as to increase the efiective length of the lever 24. Thus hysimple manipulation of the-hand wheels 5 3,55 theopenatur of (the "turbine can very readily adjust the extraction pressure in accordance with changes in the requirements of consumer I, and

change may be easily made while 'the machine is in operation Another very im-portantradvantage of. the arrangement is that such changes in the 'extraction pressure setting do notanecessitate ',t0 provide the necessary force for actuatingthe any further changes in the restoring mechanism for overtravel prevention. In this sense, the overtravel prevention mechanism is.self-adjusting, working properly regardless of changes in the extraction pressure adjusting mechanism.

.Heretofore'in cases Where awide range of adjustment'of extraction pressure at por.t.5 was required, it has been necessary for the manufacturer of extraction turbines having three-arm .governing system, as known to the prior art, to provide at least three complete alternate designs of governing system in order to permit allthe various methods of operation of which my single improved .system is capable. With the prior ar- "rangements, it was necessary to shut. down the machine and have an expert familiar with the governor make extensive alterations, even to the extent of purchasing certain re-designed parts, inorder to alter the extraction pressure. With -the'present invention, a single governing system is capable of a great variety of modes of operationand permits ready adjustment, by com- ,paratively unskilled operators, of the extraction pressure without even stopping the turbine.

using a simple direct-acting mechanical linkage connecting the arm l9a of the floating three-arm ..I9,with' the high-pressure inlet valve 4, a hydraulicservo-motor maybe interposed in order inlet valve 4. Likewise; the speed governor is may-operate: through a hydraulic relay instead ofdirectlythrough-the mechanical link id, as shown, for instance, in Fig. l of Ericson Patent 2,095,860. The extraction valve 9 may also be 2 operated, .by a. hydraulic servo-motor arrangehient. Such servo-motors are obviously equivalent to the simple mechanical links shown in the drawing, and since they are so Well known in the art,-i-it seems unnecessary to further complicate $455 the present disclosure by including such arrange- -ments;

-.'It will also be understood that in some applications .it .may not be necessary to provid'eithe overtravel limiting function for either the valve 4 or the valve 9, for either or both directions of movement. In such applications, one or more of the adjustable stops 4|, 42, 46, 41 may be omitted. Thus, if it is found not necessary to limit the overtravel of valve 9 in either direction, the abutment 48, rod 45, with the stops 46, 41 and the associated lever arm 31b may be omitted entirely from the arrangement. The remaining arm 31a with its associated stops 4!,

42 will still operate precisely as described above. Instead of actually removing the stops not needed, they may be merely backed oif so that under no conditions will they engage the associated arm of the three-arm lever 31.

It should also be noted that the invention is applicable to more complicated extraction turbines having successive turbine sections in series flow arrangement with an extraction opening between each adjacent pair of sections, as illustrated in the Ericson et al. Patent 2,111,420. The application of the improvements constituting the present invention to such extraction governors produces a regulator of enormous complexity; and it is believed that the description of such a complete system is unnnecessary 10 here because such uses of the invention will be apparent to those-familiar with such governors and the prior patented art. 7 v In vview of-thegreat variety of modifications 5 .to which the invention is amenable, I desire it to-be understood that the appended claimsare 'jintendedgto cover-all such modifications as fall within the-truejspirit and'scope of the invention.@;-.

:What-lzclaim, as-new and desire to secure by Letters Patent of the United States is:

,1. In a governing systemfor an extraction. :.turbine having ,a-floating three-arm lever for coordinating, movement of a high-pressure inlet valve and a lower-pressure extraction valve, first .;l-inkage;.,meansgconnected to a first arm of the .lever for positioningthe inletvalve, second linkage. means connected to a second arm of the leverz-for, positioning, the extraction valve and serv,o,-me, chanismadapted toposition the third arm. ofuuithe' ,lever, in accordance withchan es in extraction pressure and including extraction ;.pressure' sensing means. adapted to positionpilot .means -controlling a motor, the combination of means forautomatically limiting movement of the turbine valves comprisingsecond lever means adaptedv to producev a-crestoring action on said pilot means; and stop; means connected to move with said first and second linkages and adapted .to.engage.. said second leverwhereby the servomotor is prevented from moving the valves beyond a predetermined limiting position. v

; M2. in a governing systemgforan extraction turbine-,having ,a,,fioating three-arm lever for co- -:ordinating,movement of a high-pressure inlet .valve. and alower-pressure extraction valve, first linkage means connected to a first arm of the lever. for positioning'the inlet valve, second linkage means connected to ajsecond arm of the {lever for positioning; the extraction valve and servo-mechanism adapted toposition the third arm flthel verw n ac danc w h ha s in extraction pressure and including extraction pressure sensing means adapted to position pilot .meanscontrolling a motor, the combination of automatic limit means comprising second lever means adapted. to produce a restoring action on said pilot means, and stop means connected to .mQYe-w thslfirst li ka e, and adap d o gage said second lever whereby the servo-motor is prevented from moving the high-pressure inlet valve beyond a predetermined limiting position.

3. In a governing system for an extraction turbine having a floating three-arm lever for coordinating movement of a high-pressure inlet valve and a lower-pressure extraction valve, first linkage means connected to a first arm of the lever for positioning the inlet valve, second linkage means connected to a second arm of the lever for positioning the extraction valve and servo-mechanism adapted to position the third arm of the lever in accordance with changes in extraction pressure and including extraction pressure sensing means adapted to position pilot means controlling a motor, the combination of automatic limit means comprising second lever means adapted to produce a restoring action on said pilot means, and stop means connected to move with said second linkage and adapted to engage said second lever whereby the servomotor is prevented from moving the low-pressure extraction valve beyond a predetermined limiting position.

4. In a governing system for an extraction turbine having a floating three-arm lever for coor- 11 dinating movement of a high-pressure inlet valve and a lower-pressure extraction valve, first linkage means connected to-a first arm of the lever "for positioning the inlet valve, second linkage means connected-to a secondarm of thelever for "positioning extraction valve and servo- -mechanism adapted to position the third'arm of lever in accordance with changesin extraction pressure and including extraction pressure sensing means adapted-to position pilot means controlling a moton'the combination'of means for automatically limiting movement of the tursure inlet valve beyond predetermined limiting positions in both the'ope-ning :and the closing 1 directions, and third and fourth stop means connected to move with said secondiinkage and adapted to engage opposite sides of a second -arm of the second lever means whereby the servomotor is nrevented from moving the extraction valve beyond predetermined limiting positions in both the opening and closing directions, the third arm of the second three-arm lever means being connected to produce the direct restoring action on said pilot means. 7

5. In a governing system for an extraction turhim having a first high-pressure inlet valve and a second lowonpressure extraction valve, the

combination of a floating-three-arm lever for -c0or-dinating movement of the waives-and including means for altering the relative effective lengths of the first and second arms, first linkage means connected to the first arm for positioning the inlet valve, second linkage means connected to the second arm for positioning the extraction valve, the second linkage including variable ratio lever means for altering the rate of'chang'e of extraction valve position with change in threearm lever position, wherebythrough suitable aizl- 45 i-ustment of-the floating threearm lever and variable ratio means the extraction pressure may *be adfiusted, servo-mechanism adapted to position the third arm of the floating lever'in accord- 12 once "with changes in extraction pressure and including extraction pressure seznsingmeans constructed and arranged to position pilot means controlling .a servo-motor, and means for automatically limiting movement oi the wrblne valves comprising second lever means adapted to eflect a restoring action directly .onsaid pilot means, first adjustable stop means connected to move with the first linkage and adapted to engage a first portion of the second lever means, and second adjustable stop means connected to move with the second and adapted to engage a second spaced portion or the second lever means, whereby through adjustment of said stop means the servo-motor may bezprevenhed from moving the valves beyond predetermined limiting positions.

6. In a govermngsystem for an extraction tun 'bine having a first high-pressure inlet valve and a vsecond lower-pressnre extraction valve, a floating three-arm lever for coordinating movement of said valves, 'the'first linkage means connected to the first arm for positioning the inlet valve, second linkage'means connected to't'he seemed arm for positioning the extraction valve, and servo mechanism adapted to position the arm in accordance with changes extraction pressure and including extraction pressure sensing means, said floating three-arm lever including means for changing the efiective length of the first arm relative to the second arm, and at least one of said linkages includin variable ratio lever means for altering the rate of change of valve position with change in three-arm lever position, whereby through suitable adjustment of the floating three-arm and the variable means the extraction pressure may be adjusted.

CARL E. SEDERQUIST.

REFERENGES error) The following references are of record in the fileef this patent.

UNITED STATES PATENTS Number Name I Date 1,154,533 Moss Sept. 21, $9135 2,095,860 Ericson Oct. 12,

2,098,303 Harris Nov, .9, 1937 2,111,420 'Ericson Mar. 15,1938 

